Protist Lineage (protist + lineage)

Distribution by Scientific Domains

Selected Abstracts

Recent evolutionary diversification of a protist lineage

Ramiro Logares
Summary Here, we have identified a protist (dinoflagellate) lineage that has diversified recently in evolutionary terms. The species members of this lineage inhabit cold-water marine and lacustrine habitats, which are distributed along a broad range of salinities (0,32) and geographic distances (0,18 000 km). Moreover, the species present different degrees of morphological and sometimes physiological variability. Altogether, we analysed 30 strains, generating 55 new DNA sequences. The nuclear ribosomal DNA (nrDNA) sequences (including rapidly evolving introns) were very similar or identical among all the analysed isolates. This very low nrDNA differentiation was contrasted by a relatively high cytochrome b (COB) mitochondrial DNA (mtDNA) polymorphism, even though the COB evolves very slowly in dinoflagellates. The 16 Maximum Likelihood and Bayesian phylogenies constructed using nr/mtDNA indicated that the studied cold-water dinoflagellates constitute a monophyletic group (supported also by the morphological analyses), which appears to be evolutionary related to marine-brackish and sometimes toxic Pfiesteria species. We conclude that the studied dinoflagellates belong to a lineage which has diversified recently and spread, sometimes over long distances, across low-temperature environments which differ markedly in ecology (marine versus lacustrine communities) and salinity. Probably, this evolutionary diversification was promoted by the variety of natural selection regimes encountered in the different environments. [source]

Phylogenetic and Primary Sequence Characterization of Cathepsin B Cysteine Proteases from the Oxymonad Flagellate Monocercomonoides

ABSTRACT. Cysteine proteases are crucial for general lysosomal function and for the pathogenic mechanisms of many protistan parasites. Cathepsin B cysteine proteases are currently defined by the presence of the "occluding loop" motif and have been best characterized from humans and their parasites. Though related to a variety of pathogenic excavate flagellates, oxymonads are themselves commensals. While studying this cell biologically aberrant protist lineage, we identified 11 different cathepsin B homologues. These were found to be expressed, at comparable levels to common house-keeping genes, such as elongation factor 1-,, ,-tubulin, ,-tubulin, and glyceraldehyde phosphate dehydrogenase. Primary structure examination of the cathepsin B homologues identified putative signal peptide sequences, and the pre-, pro-, and mature domains of the protein. However, the occluding loop motif was either partially or entirely absent. Comparative genomics, sequence alignment, and phylogenetics of cathepsin sequences from across the diversity of eukaryotes demonstrated that absence of the occluding loop is not a feature exclusive to oxymonads, but is relatively common, suggesting that the "occluding loop" should no longer be used as the defining feature of the cathepsin B subfamily. Overall, this report identifies an abundant protein family in oxymonads, and provides insight both into the evolution and classification of cathepsin B cysteine proteases. [source]

Dinoflagellate mitochondrial genomes: stretching the rules of molecular biology

BIOESSAYS, Issue 2 2009
Ross F. Waller
Abstract Mitochondrial genomes represent relict bacterial genomes derived from a progenitor ,-proteobacterium that gave rise to all mitochondria through an ancient endosymbiosis. Evolution has massively reduced these genomes, yet despite relative simplicity their organization and expression has developed considerable novelty throughout eukaryotic evolution. Few organisms have reengineered their mitochondrial genomes as thoroughly as the protist lineage of dinoflagellates. Recent work reveals dinoflagellate mitochondrial genomes as likely the most gene-impoverished of any free-living eukaryote, encoding only two to three proteins. The organization and expression of these genomes, however, is far from the simplicity their gene content would suggest. Gene duplication, fragmentation, and scrambling have resulted in an inflated and complex genome organization. Extensive RNA editing then recodes gene transcripts, and trans-splicing is required to assemble full-length transcripts for at least one fragmented gene. Even after these processes, messenger RNAs (mRNAs) lack canonical start codons and most transcripts have abandoned stop codons altogether. [source]

The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists

Abstract. This revision of the classification of unicellular eukaryotes updates that of Levine et al. (1980) for the protozoa and expands it to include other protists. Whereas the previous revision was primarily to incorporate the results of ultrastructural studies, this revision incorporates results from both ultrastructural research since 1980 and molecular phylogenetic studies. We propose a scheme that is based on nameless ranked systematics. The vocabulary of the taxonomy is updated, particularly to clarify the naming of groups that have been repositioned. We recognize six clusters of eukaryotes that may represent the basic groupings similar to traditional "kingdoms." The multicellular lineages emerged from within monophyletic protist lineages: animals and fungi from Opisthokonta, plants from Archaeplastida, and brown algae from Stramenopiles. [source]